doc: update document for datetime package

docs/datetime.md

@@ -251,7 +251,7 @@ func main() {
 <b>Signature:</b>
 
 ```go
-func BeginOfWeek(t time.Time) time.Time
+func BeginOfWeek(t time.Time, beginFrom ...time.Weekday) time.Time
 ```
 <b>Example:</b>
 
@@ -414,7 +414,7 @@ func main() {
 <b>Signature:</b>
 
 ```go
-func EndOfWeek(t time.Time) time.Time
+func EndOfWeek(t time.Time, endWith ...time.Weekday) time.Time
 ```
 <b>Example:</b>
 

docs/datetime_zh-CN.md

@@ -243,12 +243,12 @@ func main() {
 
 
 ### <span id="BeginOfWeek">BeginOfWeek</span>
-<p>返回指定时间的星期开始时间</p>
+<p>返回指定时间的每周开始时间,默认开始时间星期日</p>
 
 <b>函数签名:</b>
 
 ```go
-func BeginOfWeek(t time.Time) time.Time
+func BeginOfWeek(t time.Time, beginFrom ...time.Weekday) time.Time
 ```
 <b>例子:</b>
 
@@ -406,12 +406,12 @@ func main() {
 
 
 ### <span id="EndOfWeek">EndOfWeek</span>
-<p>返回指定时间的星期结束时间</p>
+<p>返回指定时间的星期结束时间,默认结束时间星期六</p>
 
 <b>函数签名:</b>
 
 ```go
-func EndOfWeek(t time.Time) time.Time
+func EndOfWeek(t time.Time, endWith ...time.Weekday) time.Time
 ```
 <b>例子:</b>